Upwind, just gear down, keep your cadence up, and enjoy practicing your aero position. Don't even look at your speed.
It's very hard to estimate calories burned, because you don't know your watts. If you had a power meter, it'd be easy to get close. Personally, I think the numbers I get on my Polar are about right. Many people say 50 calories per mile, which takes the time/watts factor out of it. I think that's close.
On daveyboy's detraining question, I have some personal experience with that. (;-( I started training in 1995, having not done much out of zone 1 for about 25 years. It took me about 7 years to peak. If I were to detrain for 7 years now, I'd never get it back. If I detrain for 3 months, it takes me about 7 months to get it back, not 7 years. For short term detraining from a very trained state, my experience is that for every day missed over 3 days, it takes a week to get it back.
I'm saying that it's not linear, that it depends on the age of the trainee, and on the training state of the trainee.